I followed the instructions, my code compiles as expected, but there is no visible tooltip on hover over my component.
Furthermore, inspecting the web page there seems to be no reference to the tooltip js or styles on the page (the web jars do get included in the app classpath).
I also have the same problem using the exact same Java sample code provided here. I’m using Vaadin 13 beta1 (prerelease). Did you ever solve it or get a partial reply from someone/somewhere?